Any human biologists out there?

kell_riley
kell_riley Posts: 312
edited 5:30AM in Chit-Chat
I'm completing a piece of course work on the effects of meiosis on chromosomes. I wondered if anyone could look over what i have written for one of the questions and tell me if it makes sense?
It does to me but thats not saying much lol!

Meiosis is a two part cell division process of the gametes.
Prior to meiosis occurring the cell enters a phase called interphase, this is a period of growth, this is where chromosomes duplicate in preparation for cell division, the chromosomes at this point are in the form of chromatin.

Meiosis consists of two stages, Meiosis I and Meiosis II, each of the stages have subsequent phases within them.

Meiosis I

Prophase I- Chromosomes have replicated to form chromatids joined by centromere as in mitosis. In meiosis however a pair of homologous chromosomes line up together to form a tetrad. Tetrads are made up of four chromatids. At this phase chiasmata may be formed which can result in crossing over. In this phase the nuclear membranes break down, the nucleolus disappear, centrioles pull away to form the spindles

Metaphase I- The homologous pairs of chromosomes line up along the metaphase plate of the spindle.

Anaphase I- The chromosomes move to the opposite cell poles. The sister chromatids remain together as the centromeres do not split.

Telophase I- At this point there are haploid number of chromosomes at each pole, nuclear membranes form around the chromosomes and cytokinesis occurs. Two daughter cells are formed. Telophase I can be the end of division in some cases however often this is where Meiosis II occurs.

Meiosis II

Prophase II- Dispersed chromosomes shorten and become more visible again, chromosomes do not replicate any more at this phase of meiosis.

Metaphase II- Again the chromosomes line up along the metaphase plate.

Anaphase II- The sister chromatids separate at the centromeres and move toward opposite poles

Telophase II- Nuclear membranes form and cytokinesis occurs, four daughter cells are formed, each with haploid chromosomes of the parent cell. This cells will then develop into gemetes (spermatozoa or ovum)


Hope someone can help!

Replies

  • Smittyinthesun
    Smittyinthesun Posts: 120
    My Father was a Biology Professor for 43 years,he would have loved to read and discuss this with you. Unfortunately he passed away a few years ago.
  • BaliRun
    BaliRun Posts: 114 Member
    Sorry about you dad Smitty ; (

    Kell- I have a chemistry degree and took many biology classes, reading this post reminds me of all the coarse work i have tried to forget, lol!!! fun times!!!!

    You explanations look good.... I will go over some of my old text books and refresh my memory a bit more and give you tips some time tomorrow.
  • kell_riley
    kell_riley Posts: 312
    Smithy so sorry for your loss!

    Maria thank you sooooooooooooooooooooo much! look forward to your response!
  • cupotee
    cupotee Posts: 181 Member
    Sure :)
    Meiosis is a two part cell division process of the gametes.
    Prior to meiosis occurring the cell enters a phase called interphase, this is a period of growth, this is where chromosomes duplicate in preparation for cell division, the chromosomes at this point are in the form of chromatin.

    It should be a two part division process FORMING gametes. The gametes themselves don't divide. Also, i would say "this is where CHROMATIN duplicate" instead of correcting "chromosome" at the end of the sentence. Maybe mention that Interphase is the longest phase of the cell cycle?
    Meiosis consists of two stages, Meiosis I and Meiosis II, each of the stages have subsequent phases within them.
    "Subsequent" means "after" or "following". It's not a great word to use here. How about, each phase "progresses in stages"?
    Meiosis I

    Prophase I- Chromosomes have replicated to form chromatids joined by centromere as in mitosis. In meiosis however a pair of homologous chromosomes line up together to form a tetrad. Tetrads are made up of four chromatids. At this phase chiasmata may be formed which can result in crossing over. In this phase the nuclear membranes break down, the nucleolus disappear, centrioles pull away to form the spindles
    1. "chromosomes have replicated...": I would put, Chromatin condenses into chromatids. Sister chromatids join AT the centromere to form chromosomes.
    2. "centrioles pull away...": Spindle formation is independent of migration. So put that in two separate sentences, eg. Centrioles migrate to the poles. Spindle fibers form, connecting to the centromeres of the chromosome.
    Metaphase I- The homologous pairs of chromosomes line up along the metaphase plate of the spindle.

    Anaphase I- The chromosomes move to the opposite cell poles. The sister chromatids remain together as the centromeres do not split.

    Telophase I- At this point there are haploid number of chromosomes at each pole, nuclear membranes form around the chromosomes and cytokinesis occurs. Two daughter cells are formed. Telophase I can be the end of division in some cases however often this is where Meiosis II occurs.

    1. they line up at the metaphase plate of the cell, i think. You can also call it the "equator" of the cell. I've never heard of "metaphase plate of the spindle."
    2. Make sure you specify that homologous chromosome pairs are split up, with one chromosome of each pair traveling towards one cell poles.
    3. Telophase I will never be the end of division in complete meiosis.
    Meiosis II

    Prophase II- Dispersed chromosomes shorten and become more visible again, chromosomes do not replicate any more at this phase of meiosis.

    Metaphase II- Again the chromosomes line up along the metaphase plate.

    Anaphase II- The sister chromatids separate at the centromeres and move toward opposite poles

    Telophase II- Nuclear membranes form and cytokinesis occurs, four daughter cells are formed, each with haploid chromosomes of the parent cell. This cells will then develop into gemetes (spermatozoa or ovum)
    1. "haploid" is used to describe a cell, not chromosomes.

    Also, idk about how your teacher taught it, but cytokinesis occurs simultaneously and independently of the phases of meiosis. It just happens to end around telophase. Cytokinesis is not part of meiosis, but part of the cell cycle.

    hope this helps :)
  • kell_riley
    kell_riley Posts: 312
    Thank you very much cupotee! It's a big help, I've got a few bits to change there lol!
    Again thank you!!
  • davidsadler86
    davidsadler86 Posts: 22
    Do you need to mention genetic diversity? Crossing over and orientation of the chromatids etc?
  • kell_riley
    kell_riley Posts: 312
    Dave, i don't think so, the question is Describe what happens to chromosomes in meiosis.
    We've not covered crossing over in much detail, just that it happens in meiosis. Genetic diversity is the next assignment to come. When you say orientation of the chromatids what do you mean?
  • koosdel
    koosdel Posts: 3,317 Member
    Man... they some big words in this post.
  • kell_riley
    kell_riley Posts: 312
    LOL! its not so bad when you get the hang of things!
    That my friend is how your sperm cells are made! :laugh:
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